1. Field of the Invention
The invention relates to video display method and video display apparatus which can express a front/rear feeling and a stereoscopic feeling of an object to be displayed when a video image based on an input video signal is displayed.
2. Description of the Related Art
As a system having the highest realization among stereoscopic display systems, there is a stereoscopic display system using right/left parallax information. According to such a system, two cameras are used upon photographing and a video image for the left eye and a video image for the right eye are photographed so as to have parallax information. By reproducing the video images so that two images are separately projected to the right and left eyes, a stereoscopic display can be performed.
FIGS. 1A and 1B show a principle of the stereoscopic operation using a binocular (right/left) parallax. Images obtained by shifting a left-eye video image 3L and a right-eye video image 3R in the horizontal direction are displayed on a display plane 1. Usually, a focal point (a point at which the right and left lines of sight cross: such a point is called a point where the vergences are matched) of both of the left and right eyes (2L, 2R) and a focal point (a point where the adjustment of the eye in case of a single eye is matched) of each eye (2L, 2R) are located at the same position. Specifically speaking, in case of a CRT or the like, the CRT surface corresponds to the location where the vergences and the adjustments are matched. In case of a projector or the like, the screen corresponds to the location where the vergences and the adjustments are matched.
FIG. 1A shows a case of a cross vergence. In this case, the video image 3R shifted to the left is allowed to be projected to the right eye 2R and the video image 3L shifted to the right is allowed to be projected to the left eye 2L. At this time, an image is synthesized in the head as if an object existed at a location where the vergences of the right and left eyes are matched. Such an imaginary image 4A is seen as if it was projected to the front side from the display plane 1. On the other hand, FIG. 1B shows a case of a parallel vergence (non-cross vergence). In this case, the video image 3L shifted to the left is allowed to be projected to the left eye 2L and the video image 3R shifted to the right is allowed to be projected to the right eye 2R. In the parallel vergence, an imaginary image 4B is synthesized to the rear side from the display plane 1.
A technique for enabling a stereoscopic feeling to be obtained even in an ordinary two-dimensional image by using the principle of the right/left parallax is an emphasis of a stereoscopic feeling using an effect of Pulfrich. The effect of pendulum of Pulfrich denotes "when an object which reciprocates to the right and left in the vertical plane in front of the eyes is observed by both eyes while a filter (ND filter) for reducing light is attached in front of one eye, the object is seen as if it moved with a depth while drawing a locus on an ellipse in a manner such that the object exists before and behind the plane". For example, as shown in FIG. 2, in a state where an ND filter 5 is attached in front of the left eye 2L, a pendulum which reciprocates to the right and left in a plane 6 is observed. When the pendulum moves from the right to the left, the pendulum passes in front of the plane 6. On the contrary, when the pendulum moves from the left to the right, the pendulum passes through the rear side from the plane 6. Consequently, the pendulum is observed as if the locus of the pendulum formed an elliptical orbit 7.
The effect of pendulum of Pulfrich occurs because when signals from the eyes are transmitted to the cerebrum, the left eye 2L for which the light is weakened has a time delay as compared with the right eye 2R for which the light is not weakened. That is, in an example of FIG. 2, when the pendulum moves from the right to the left and is located at a position of q, the signal from the left eye 2L is delayed, so that at this moment, the left eye 2L recognizes as if the pendulum existed at a position of p. In this manner, a binocular parallax occurs and the observer feels as if the pendulum existed at a position of N by the cross vergence shown in FIG. 1A mentioned above. On the contrary, when the pendulum moves from the left to the right and exists at the position of q, the left eye 2L recognizes as if the pendulum existed at a position of r. Due to the binocular parallax, the observer feels as if the pendulum existed at a position of F by the parallel vergence shown in FIG. 1B.
Hitherto, as a method of enhancing the stereoscopic feeling of an ordinary 2-dimensional video image, a method using the foregoing Pulfrich's effect has been known. The above method, however, has a drawback such that a stereoscopic feeling (depth feeling) of only the object which moves in a specific direction is merely expressed and the effect is not derived in a still portion. Such a method also has a drawback such that the stereoscopic feeling is influenced by a moving speed and its direction of the object. In other words, the depth feeling changes depending on the moving speed and the front/rear side is unconditionally determined by the moving direction. As mentioned above, according to the conventional stereoscopic feeling emphasizing method, the stereoscopic feeling (depth feeling) for only an object which moves in a specific direction can be correctly expressed.